As a prior art extendible whip antenna used for a hand-held two-way radio apparatus such as a portable cellular telephone, etc. there are known those disclosed e.g. in JP-A-Hei 2-271701, U.S. Pat. No. 4,121,218, etc.
The whip antenna disclosed in JP-A-Hei 2-271701 utilizes a 1/2-wave length spring antenna element and a 1/2-wave length fixed helical element capacitively coupled therewith. When it is not used, the spring antenna element is accommodated in a case of the hand-held two-way radio apparatus through the helical antenna so that a state where communication is feasible is kept by the helical antenna element. On the other hand, when it is used, the spring antenna element is extended.
However problems in a whip antenna thus constructed are that fabrication of the spring antenna element is not easy in practice and that it is difficult to obtain a predetermined degree of coupling with the helical antenna.
On the other hand, the whip antenna disclosed in the U.S. patent specification stated above is constructed similarly to that described previously except that a linearly extendible whip antenna element is used in lieu of the spring antenna element. In this antenna the whip antenna element extended at use is capacitively coupled with the helical antenna element.
A problem in this case consists in that since matching of the whip antenna with a radio circuit is adjusted by varying the length of the whip antenna element and the gap (capacitive coupling) between the two antenna elements, regulation thereof is tedious and it is difficult to expect to effect it with a high precision.
Further, as a problem common to the two antennas described above, it should be noted that since the helical antenna element is of 1/4-wave length sensitivity thereof when the whip antenna element is accommodated in the case of the radio circuit is low and that the received frequency band thereof is narrow. This is due to the fact that they are so constructed that the two antenna elements are fed through capacitive coupling in series.